blob: 0ac2806e3b740ad1fe4604d8734018c40fc80b5e [file] [log] [blame]
use crate::cert::{certificate_serial_number, Cert};
use crate::{
cert::{parse_cert_internal, EndEntityOrCa},
der, Error,
/// A trust anchor (a.k.a. root CA).
/// Traditionally, certificate verification libraries have represented trust
/// anchors as full X.509 root certificates. However, those certificates
/// contain a lot more data than is needed for verifying certificates. The
/// `TrustAnchor` representation allows an application to store just the
/// essential elements of trust anchors. The `webpki::trust_anchor_util` module
/// provides functions for converting X.509 certificates to to the minimized
/// `TrustAnchor` representation, either at runtime or in a build script.
pub struct TrustAnchor<'a> {
/// The value of the `subject` field of the trust anchor.
pub subject: &'a [u8],
/// The value of the `subjectPublicKeyInfo` field of the trust anchor.
pub spki: &'a [u8],
/// The value of a DER-encoded NameConstraints, containing name
/// constraints to apply to the trust anchor, if any.
pub name_constraints: Option<&'a [u8]>,
/// Trust anchors which may be used for authenticating servers.
pub struct TlsServerTrustAnchors<'a>(pub &'a [TrustAnchor<'a>]);
/// Trust anchors which may be used for authenticating clients.
pub struct TlsClientTrustAnchors<'a>(pub &'a [TrustAnchor<'a>]);
impl<'a> TrustAnchor<'a> {
/// Interprets the given DER-encoded certificate as a `TrustAnchor`. The
/// certificate is not validated. In particular, there is no check that the
/// certificate is self-signed or even that the certificate has the cA basic
/// constraint.
pub fn try_from_cert_der(cert_der: &'a [u8]) -> Result<Self, Error> {
let cert_der = untrusted::Input::from(cert_der);
// XXX: `EndEntityOrCA::EndEntity` is used instead of `EndEntityOrCA::CA`
// because we don't have a reference to a child cert, which is needed for
// `EndEntityOrCA::CA`. For this purpose, it doesn't matter.
// v1 certificates will result in `Error::BadDER` because `parse_cert` will
// expect a version field that isn't there. In that case, try to parse the
// certificate using a special parser for v1 certificates. Notably, that
// parser doesn't allow extensions, so there's no need to worry about
// embedded name constraints in a v1 certificate.
match parse_cert_internal(
) {
Ok(cert) => Ok(Self::from(cert)),
Err(Error::UnsupportedCertVersion) => parse_cert_v1(cert_der).or(Err(Error::BadDer)),
Err(err) => Err(err),
fn possibly_invalid_certificate_serial_number(input: &mut untrusted::Reader) -> Result<(), Error> {
// * Conforming CAs MUST NOT use serialNumber values longer than 20 octets."
// * "The serial number MUST be a positive integer [...]"
// However, we don't enforce these constraints on trust anchors, as there
// are widely-deployed trust anchors that violate these constraints.
skip(input, der::Tag::Integer)
impl<'a> From<Cert<'a>> for TrustAnchor<'a> {
fn from(cert: Cert<'a>) -> Self {
Self {
subject: cert.subject.as_slice_less_safe(),
spki: cert.spki.value().as_slice_less_safe(),
name_constraints:|nc| nc.as_slice_less_safe()),
/// Parses a v1 certificate directly into a TrustAnchor.
fn parse_cert_v1(cert_der: untrusted::Input) -> Result<TrustAnchor, Error> {
// X.509 Certificate:
cert_der.read_all(Error::BadDer, |cert_der| {
der::nested(cert_der, der::Tag::Sequence, Error::BadDer, |cert_der| {
let anchor = der::nested(cert_der, der::Tag::Sequence, Error::BadDer, |tbs| {
// The version number field does not appear in v1 certificates.
skip(tbs, der::Tag::Sequence)?; // signature.
skip(tbs, der::Tag::Sequence)?; // issuer.
skip(tbs, der::Tag::Sequence)?; // validity.
let subject = der::expect_tag_and_get_value(tbs, der::Tag::Sequence)?;
let spki = der::expect_tag_and_get_value(tbs, der::Tag::Sequence)?;
Ok(TrustAnchor {
subject: subject.as_slice_less_safe(),
spki: spki.as_slice_less_safe(),
name_constraints: None,
// read and discard signatureAlgorithm + signature
skip(cert_der, der::Tag::Sequence)?;
skip(cert_der, der::Tag::BitString)?;
fn skip(input: &mut untrusted::Reader, tag: der::Tag) -> Result<(), Error> {
der::expect_tag_and_get_value(input, tag).map(|_| ())